Heat exchanger agitator



16, 1958 F. M. YOUNG HEAT EXCHANGER AGITATOR Filed Feb. 25, 1957 INVENTOR- ATTORNEYS.

United States Patent HEAT EXCHAN GER AGITATOR Fred M. Young, Racine, Wis., assignor to Young Radiator Company, Racine, Wis., a corporation of Wisconsin Application February 25, 1957, Serial No. 641,933

3 Claims. (Cl. 138-38) This invention relates to turbulence or agitator strips for the tubes of fluid heat-exchangers, particularly those for cooling the oil required in high-powered, high-heatproducing engines.

The comparatively-recent and constantly-increasing development of high-powered, heat-producing engines for transportation, on land, water, and in the air, for earthmoving machinery, and for military equipment, has been made possible, in part, because the producers of heat exchange equipment have been alert to the requirements for units requiring the minimum of space with the maximum of efliciency.

The use of smaller units obviously has necessitated the employment of smaller tubing. Smaller tubing, in turn has necessitated higher pressures in an attempt to attain the requisite temperature drop in the fluid to be cooled. However, this has presented some problems in heatexchanger construction.

It is well known that in tubular heat exchangers the tendency toward the equalization of temperature between the fluid flowing through the tubes and the fluid enveloping the tubes takes place through the tube wall. Where the fluid is flowing through the tube under pressure, it is also well known that the column of fluid in efiect comprises a concentric series of films or laminae, from the core to the circumference coincident with the inner face of the tube wall. Under pressure these concentric films or laminae tend to move successively slower from the core outwardly to the circumference where the film or laminae, in frictional contact with the inner face of the tube wall, moves the slowest; in fact tends almost to immobility. Obviously, therefore, under such conditions the heat dissipation of the films or laminae of fluid is successively less from the circumference inwardly to the core, where the heat dissipation is at a very minimum. To overcome this decreasing heat dissipation, from the wall of the tube inwardly to the core of the fluid column, it has been .common practice to incorporate in the tubes some kind of fin, bafile, or turbulence strip. These are designed to slice or break-up and radially deflect these concentric fluid films or laminae so as to effect contact of all the fluid molecules with the heat-dissipating tube wall. The construction of such devices has followed a myriad of patterns in an attempt to get reasonable hightemperature drop with a minimum pressure drop.

During the years of this development of these smaller heat-exchange units for high-power heat engines, the research departments of the larger heat-exchange producers, through study and experimentation, have been seeking to develop internal-fin or agitator structures that would achieve the very maximum of temperature drop with the lowest possible pressure drop, and which, at the same time, would be capable of extremely low-cost production.

The main objects of this invention, therefore, are to provide an improved form of internal agitator especially adapted for the smaller diameter tubes of heat exchangers; to provide an improved form of agitator of this kind capable of achieving a most practical high-temperature drop without too great a build-up of pressure; and to provide an agitator of this kind which is so simple as to make' its manufacture very economical and its use exceedingly facile and effective.

In the accompanying drawings:

Fig. l is a perspective view of a flat strip of metal showing the disposition of the slits which allow for upsetting or bending over marginal portions to provide triangularlyshaped lobes with transversely-disposed rectangularshaped, flanges;

Fig. 1a is a perspective view of modification of the form shown in Fig. 1;

Fig. 2 is a perspective view of such a strip in twisted form after the formation of the lobes;

Fig. 3 is an enlarged, longitudinal, sectional view of a portion of tubing with this improved form ofagitator in place therein;

Fig. 3a is a section similar to Fig. 3 but showing the lobe as formed in Fig. 1a; and

Fig. 4 is a transverse, sectional view of the tube and agitator taken on the plane of the line 4-4 of Fig. 3.

The essential concept of this invention involves a strip of metal marginal portions of which are struck out to form flanged lobes transversely disposed to the plane of the strip along opposite lateral edges, the strip being twisted so that the flanged lobes are arranged in predetermined longitudinallyand circumferentially-spaced relationship.

The herein shown agitator, embodying the foregoing concept, comprises a thin, narrow, flat strip 5 having a plurality of right-angle slits 6 and 7 cut in from and inwardly parallel with the opposite lateral edges whereby marginal portions of the strip 5 at one side of each such slits 6 and 7 are bent out from the plane of the strip to form trapezoidal-shaped, right-angularly-disposed flanged lobes 8, the strip 5 then being twisted so that the succession of lobes 8 along the strip 5 are disposed substantially ninety degrees apart circumferentially around the interior of a tube 9.

The strip 5 may be any kind of metal which the incidents of economic manufacture and eflicient use may dictate. For some types of heat-exchanger the metal may have to be thin as 0.017 inch and narrow enough to fit in a tube 76 outside diameter.

As clearly shown in the drawings, the right-angle slits 6 and 7 are cut in from and parallel with the opposite lateral edges with successive slits 6 and 7 being arranged along opposite edges of the strip. The cuts 6 are normal to the longitudinal axis of the strip 5 and are of a length less than half the width of the strip 5, preferably approximately one-third the width of the strip. The slits 7 are substantially the same length as the slits 6.

The lobes 8 are formed by bending over the marginal portions of the strip 5, at right angles to the plane of the strip, along lines 10 from the inner end of each slit 7 diagonally to the adjacent lateral edge of the strip and then bending over the free end of each lobe 8 to form a rectangular flange section 11 disposed at right angles to a triangular section 12. (See Fig. 2.) The plane of each lobe section 12 is thus disposed at a slight incline to the longitudinal axis of the strip 5, as is most apparent from the drawings.

After such forming of the strip 5, with its flanged lobes 8, the strip is so twisted that the lobes 8 are spaced substantialy ninety degrees apart circumferentially of the strip (see Fig. 4) in their longitudinal disposition along the strip.

With an agitator of this formation placed in a tube 9, and the fluid flowing through the tube in the direction of the arrow 13 in Fig. 3, the twist of the strip tends to produce a swirling, centrifugally-outward movement of the flow. Such swirling centrifugal flow precludes the possibility of a freely-moving, heat-retaining central core along the axis of the tube 9. The lobes 8 tend to slice up that centrifugally-swirling flow and accentuate the 1mpingement thereof against the wall of the tube 9, where the heat is most readily extracted from the fluids. The lobe flange sections 11 obviously present obstructions in this centrifugally-swirling flow and set up a turbulence that further deflects the flow outwardly toward the wall of the tube 9.

On occasion, it may be found expedient to have an aperture 14 'formed in the flange 11 to further break up and intensify the turbulence in the flow through the tube. Also, on occasion, when a somewhat less agitation of the flow is desired, the bending of the lobes 8 to form the flange sections 11 could be omitted. In that case the lobes 8 would comprise only a longer triangular section 12.

Variations and modifications in the details of structure and arrangement of the parts may be resorted to within the spirit and coverage of the appended claims.

I claim:

1. An agitator for tubular heat exchangers comprising, a thin, narrow, flat strip of sheet metal having slits cut therein from the opposite lateral edges normal to the longitudinal axis of the strip and longitudinally along the strip, marginal portions of the strip being bent outwardly from the plane of the strip along lines extending diagonally outward from the termini of the respective longitudinal slits remote from the respective normal slits to points on the adjacent lateral edges of the strip to form a series of trapezoidal-shaped lobes spaced longitudinally along the opposite lateral edges of the strip, the ends of the lobes being bent to form transverse flanges.

2. An agitator for tubular heat exchangers comprising, a thin, narrow, flat strip of sheet metal having slits cut therein from the opposite lateral edges and longitudinally along the strip, the slits extending inwardly from the strip edges being normal to the longitudinal axis of the strip a distance less than half the width of the strip, the longitudinally-extending slits being substantially equal to the length of the slits extending transversely of the strip, marginal portions of the strip being bent outwardly from the plane of the strip along lines extending diagonally outward from the termini of the respective longitudinal slits remote from the respective normal slits to points on the adjacent lateral edges of the strip to form a series of trapezoidal-shaped lobes spaced longitudinally along the opposite lateral edges of the strip, the ends of the respective lobes being bent to form transversely-disposed flanges, the flanges each having an aperture formed therein, the strip being twisted to locate the lobes in circumferentially-spaced relationship.

3. An agitator for tubular heat exchangers comprising, a thin, narrow, flat strip of sheet metal having slits cut therein from the opposite lateral edges and longitudinsb 1y along the strip, the slits extending inwardly from the strip edges being normal to the longitudinal axis of the strip a distance less than half the width of the strip, the longitudinally-extending slits being substantially equal to the length of the slits extending transversely of the strip, marginal portions of the strip being bent outwardly from the plane of the strip along lines extending diagonally outward from the termini of the respective longitudinal slits remote from the respective normal slits to points on the adjacent lateral edges of the strip to form a series of trapezoidal-shaped lobes spaced longitudinally along the opposite lateral edges of the strip, the ends of the respective lobes being bent to form transversely-disposed flanges, the strip being twisted to locate the lobes in circumferentially-spaced relationship.

References Cited in the file of this patent UNITED STATES PATENTS 1,056,373 Segelken Mar. 18, 1913 2,091,274 Eggleston Aug. 31, 1937 2,677,394 Brinen May 4, 1954 2,691,991 Schutt et al. Oct. 19, 1954 

